Such a method is for example known from WO 98/39640.
According to this method, the first heat input element is a line created by a laser, moved on the surface of the part. A detection zone is also moved on the surface of the part, following the trajectory of the heat input element, with a positive or negative time delay. The detection zone is continuously examined by the first photosensitive surface.
To inspect the first zone, it is necessary to perform four successive scans: an outgoing journey in the first direction, a return in the first direction, an outgoing journey in a second direction, which may be perpendicular to the first, and a return in the second direction.
The examination method is therefore relatively long: the examination time is about 3 to 4 hours per m2 of surface area to be inspected.